1. Field of the Invention
The present invention relates to a technical field of a navigation apparatus, and more particularly to a technical field of an apparatus for evaluating positioning data obtained by GPS navigation.
2. Description of the Related Art
In navigation apparatuses, as one of techniques for following up a vehicle or the like by detecting its current position, a positioning method which obtains a position of a vehicle based on a satellite signal (GPS signal) transmitted from a GPS (Global Positioning System) satellite has been generally widespread (which will be referred to as GPS navigation hereinafter).
The accuracy of a position obtained by positioning calculation in the GPS navigation is determined by the satellite arrangement of satellites (basically, not less than four) which transmit GPS signals and the measurement accuracy of a distance from a vehicle, which has received the GPS signals, to each GPS satellite (which will be referred to as a pseudo-range hereinafter).
Further, in recent years, there has been adopted a method which carries out map matching with a map data base by using both the GPS navigation and dead-reckoning which obtains a traveling trajectory by using a gyro sensor and a vehicle speed sensor (which will be simply referred to as dead-reckoning hereinafter).
In such a technique, in case of using a positioning result actually obtained by the GPS navigation in a car navigation apparatus, when a vehicle""s own position obtained by the dead-reckoning or map matching largely deviates from a positioning result obtained by the GPS for example, the vehicle""s own position is reset to a position of this positioning result, or this result is utilized for selecting a matching position candidate used in map matching.
On the other hand, since the positioning result actually obtained by the GPS navigation includes an error of, e.g., the system or arrangement of the GPS satellites, an error in the positioning result must be taken into consideration in order to use the result positioned by the GPS signal for evaluation of the vehicle""s own position.
More specifically, for example, there is a method which uses an error coefficient called a DOP (Dilution of Precision) value determined by arrangement of the GPS satellites and enables the positioning result obtained by the GPS navigation. This method enables the positioning result obtained by the GPS navigation only when the DOP value in the received GPS signal is equal to or below a fixed value.
When a distance to a satellite observed in sole positioning of each GPS satellite includes an error at a fixed level, this DOP value is an index value used for estimating how this error affects the positioning result. As typical DOP values, there are a DOP (HDOP) value in the horizontal direction, a DOP (VDOP) value in the vertical direction and a DOP (PDOP) value in the horizontal/vertical directions.
Furthermore, there is a method which calculates a range in which a vehicle may possibly exist (positioning error range (which will be simply referred to as an error range hereunder)) based on the DOP value and evaluates the inside of this range as a correct position of the vehicle.
In this method, a radius of a circle is obtained by a product of the DOP value and a measurement error in a pseudo-range in each of a plurality of satellites, i.e., (Expression 1), and the vehicle""s own position is evaluated with an area in the circle (which will be referred to as an error distribution circle hereinafter) range generated by the radius being determined as a range in which the vehicle may exists.
Error distribution circuit (radius)=HDOPxc3x97Measurement error of pseudo-rangexe2x80x83xe2x80x83(1)
It is to be noted that a maximum value in the measurement errors of a plurality of obtained pseudo-ranges or a mean value of the measurement errors of the respective pseudo-ranges is used as the measurement error of the pseudo-range used for calculation in this method.
On the other hand, there is a method which obtains the error range determined by the GPS satellite arrangement by calculating a probability error ellipse (which will be referred to as an error ellipse hereinafter) without using the DOP value.
According to the method using the error ellipse, an error ellipse which is an error range is calculated based on the arrangement of the GPS satellites used for positioning and a pseudo-range error in each GPS satellite, and the vehicle""s own position is evaluated as an area that the vehicle may exists in any range in the error ellipse.
This error ellipse shows the distribution of the position error which two-dimensionally distributes when components of the position error in a positioning result in the latitudinal direction and the longitudinal direction normally distribute. Specifically, calculation is carried out by using a standard deviation of an error in the latitudinal direction, a standard deviation of an error in the longitudinal direction and the correlation function of the respective standard deviations. Moreover, as represented by Expression (2), in regard to the error ellipse actually used for accuracy evaluation, an ellipse (true error ellipse) is calculated by multiplying the error ellipse calculated as described above by the measurement error of the pseudo-range in the actual GPS satellite.
Error ellipse (true)=Error ellipse (for example, an error is assumed as 1 m)xc3x97Measurement Error of Pseudo-rangexe2x80x83xe2x80x83(2)
Incidentally, assuming that measurement errors of distances to all the satellites are constant (for example, 1 m), the shape of ellipse (long axis, short axis, inclination) can be readily calculated.
In addition, the error ellipse presumed to be 1 m is a reference error ellipse generated by assuming that the pseudo-range error in each GPS signal is 1 m. The true range of the error ellipse can be, therefore, represented by multiplying the error ellipse presumed to be 1 m by the measurement error of the pseudo-range in the GPS signal.
It is often the case that a value obtained by adding an accuracy value of the pseudo-range error broadcasted from each satellite (which will be referred to as UERE (User Equivalent Range Error)) and the measurement error caused due to noise generated in the GPS receiver is used as the error value of the pseudo-range of the satellite. The validity of the vehicle""s own position can be judged based on the relationship between the ellipse and the vehicle""s own position.
In case of the method using the above-described DOP value, however, the error distribution actually outputted by the GPS receiver becomes an ellipse instead of a circle because of the arrangement of the GPS satellites used for positioning, and hence there is a problem that the vehicle""s own position can not be correctly evaluated (when the ellipse becomes oblong in particular).
For example, as shown in FIG. 4, assuming that the vehicle""s own position calculated by the dead-reckoning is a point a and a positioning result positioned based on the GPS signal is a point b, since the point a is included in both the error distribution circle A obtained by the DOP value generated based on the point b of the positioning result and the error ellipse B obtained by the arrangement of the GPS satellites generated based on the point b of the positioning result, an error is not produced in an evaluation result of the vehicle""s own position. However, when the vehicle""s own position is a point c for example, the point b of the evaluation result differs. That is, although the vehicle""s own position is evaluated as inappropriate in the error ellipse representing the further accurate error range, it is determined as appropriate in the error distribution circle.
Additionally, in the method using the error ellipse mentioned above, there is not included the measurement error in the pseudo-range which inherently occurs depending on a position of each GPS receiver such as multi-path. Therefore, in a place where the large multi-path occurs during traveling in a urban district or the like, matching between the accuracy indicated by the error ellipse, i.e., the error range obtained by the calculation of Expression (2) and the actually generated error range can not be achieved, and evaluation of the vehicle""s own position can not be appropriately carried out.
For example, as shown in FIG. 5, assuming that a position at which the vehicle""s own position obtained by the dead-reckoning or the like and the true vehicle""s own position are matched is a point d and a positioning result positioned based on the GPS signal without occurrence of the multi-path is a point e, the point d exists in an error ellipse C generated with the point e as a reference, and hence the point d is evaluated as being appropriate as the vehicle""s own position, which does not lead to a problem. However, the multi-path occurs due to reflection by an obstacle when receiving the GPS signal, the positioning result obtained from the GPS signal is shifted from the point e to, e.g., a point f due to occurrence of the multi-path. At this moment, since the influence of occurrence of the multi-path is not reflected to Expression (2), the size of an error ellipse D is still the same as that of the error ellipse C. Thus, the point d of the vehicle""s own position obtained by the dead-reckoning or the like is judged as inappropriate.
As a countermeasure when the multi-path occurs, although a method which estimates the pseudo-range as being larger than a regularly calculated value can be considered, this results in constant enlargement of the error ellipse, thereby leading to a different problem that the reliability of evaluation of the vehicle""s own position is lowered.
In view of the above-described problems, it is an object of the present invention to provide an error range judging apparatus capable of correctly evaluating a positioning result even if a pseudo-error which inherently occurs depending on a position of a GPS receiver, and a navigation apparatus utilizing this apparatus.
The above object of the present invention can be achieved by a positioning error range setting apparatus of the present invention. The apparatus is provided with: a calculating device for calculating a geographical position of a receiver by calculating a pseudo-range between said receiver and each of a plurality of transmitters based on a positioning signal transmitted from each of a plurality of said transmitters; a detecting device for detecting whether each said positioning signal is a signal received with occurrence of multi-path; and a determining device for determining a positioning error range of said geographical position based on arrangement of a plurality of said transmitters, a positioning error generated when calculating said pseudo-range and a detection result in said detecting device.
According to the present invention, a calculating device calculates a geographical position of a receiver by calculating a pseudo-range between the receiver and each of a plurality of transmitters based on positioning signals transmitted from a plurality of the transmitters, s detecting device detects whether each positioning signal is a signal received with occurrence of multi-path, and a determining device determines a positioning error range of the geographical position based on arrangement of a plurality of the transmitters, a positioning error generated when calculating the pseudo-range and a detection result of the detecting device.
Therefore, since the positioning error range of the geographical position can be calculated based on arrangement of a plurality of the transmitters, the positioning error generated when calculating the pseudo-range and the detection result of multi-path, an appropriate positioning error range can be obtained taking the influence of the multi-path into consideration even if the multi-path occurs when receiving the positioning signals.
In one aspect of the present invention, the positioning error is acquired based on accuracy information of said pseudo-range that the positioning signal has.
According to this aspect, the accuracy of the calculated pseudo-range can be reflected to the positioning error range, the appropriate positioning error range can be calculated.
In another aspect of the present invention, the detecting device detects an error in the pseudo-range of a positioning signal received with occurrence of multi-path and calculates the positioning error based on said error in the pseudo-range.
According to this aspect, the detecting device detects an error in the pseudo-range of the positioning signal received with occurrence of multi-path and calculates a positioning error based on the error in the pseudo-range.
Therefore, since the positioning error range of the geographical position in the receiver can be calculated based on the error in the pseudo-range generated due to the multi-path even if the multi-path is detected when receiving the positioning signal, the influence of the multi-path can be reflected to the positioning error range, thereby obtaining the appropriate positioning error range.
In further aspect of the present invention, the error in the pseudo-range of the positioning signal received with occurrence of multi-path is compared with a value obtained by using the accuracy information of the pseudo-range that the positioning signal has, and the larger value in comparison is determined as the positioning error.
According to this aspect, an error the a pseudo-range of the positioning signal received with occurrence of multi-path is compared with a value obtained by using accuracy information of the pseudo-range of the positioning signal, and the value which is larger in comparison is determined as a positioning error.
Therefore, when the multi-path is detected when receiving the positioning signal, the influence of the multi-path can be reflected to the positioning error range. Further, when it is not detected, the accuracy of the calculated pseudo-range can be reflected to the positioning error range, thereby obtaining the appropriate positioning error range.
In further aspect of the present invention, the positioning error is calculated based on the error in the pseudo-range of the positioning signal received with occurrence of multi-path and the value obtained by using the accuracy information of the pseudo-range that the positioning signal has.
According to this aspect, the positioning error is calculated based on an error in the pseudo-range of the positioning signal received with occurrence of multi-path and accuracy information of the pseudo-range that the positioning signal has.
Therefore, the accuracy of the calculated pseudo-range can be reflected to the positioning error range, and the influence of the multi-path can be reflected to the positioning error range when the multi-path is detected, thereby calculating the appropriate positioning error range.
In further aspect of the present invention, the error in the pseudo-range of the positioning signal received with occurrence of multi-path is generated based on a differential value between a predicted value predicted by using an already calculated pseudo-range and the pseudo-range calculated by the calculating device.
According to this aspect, an error in the pseudo-range of the positioning signal received with occurrence of multi-path is generated based on a differential value between a predicted value which is predicted from the already calculated pseudo-range and the pseudo-range calculated by the calculating device.
Accordingly, the accuracy of the error in the pseudo-range generated due to the multi-path can be improved, and the positioning error range calculated when the multi-path is detected can be appropriately obtained.
In further aspect of the present invention, the differential value is less than a predetermined reference value, the value obtained by using the accuracy information is determined as the positioning error.
According to this aspect, when the differential value is less than a predetermined reference value, a value obtained by accuracy information is determined as a positioning error.
Therefore, when the error in the pseudo-range generated due to the multi-path is smaller than a value obtained by using the accuracy information in the positioning signal, the positioning error range can be calculated by using the accuracy information that the positioning signal has, and hence the positioning error range can be appropriately calculated when the multi-path is accidentally detected.
The above object of the present invention can be achieved by a navigation apparatus of the present invention. The apparatus is provided with: a positioning error range setting device comprising: a calculating device for calculating a geographical position of a receiver by calculating a pseudo-range between said receiver and each of a plurality of transmitters based on a positioning signal transmitted from each of a plurality of said transmitters; a detecting device for detecting whether each said positioning signal is a signal received with occurrence of multi-path; and a determining device for determining a positioning error range of said geographical position based on arrangement of a plurality of said transmitters, a positioning error generated when calculating said pseudo-range and a detection result in said detecting device; and an evaluating device for evaluating a position of a movable body positioned by dead-reckoning based on a geographical position of said receiver estimated based on said positioning signal and said positioning error range calculated by said positioning error range setting device.
According to this invention, a position of a movable body positioned by dead-reckoning is evaluated based on a geographical position of a receiver estimated based on a positioning signal and a positioning error range calculated by a positioning error range setting apparatus.
Thus, a position of a movable body positioned by dead-reckoning can be evaluated based on a positioning error range to which the influence of multi-path is reflected, thereby improving the position accuracy in navigation.
The above object of the present invention can be achieved by a positioning error range setting method of the present invention. The method is provided with: a calculation process of calculating a geographical position of a receiver by calculating a pseudo-range between said receiver and each of a plurality of transmitters based on a positioning signal transmitted from each of a plurality of said transmitters; a detection process of detecting whether each said positioning signal is a signal received with occurrence of multi-path; and a determination process of determining a positioning error range of said geographical position based on arrangement of a plurality of said transmitters, a positioning error generated when calculating said pseudo-range and a detection result in said detection process.
According to the present invention, a calculation step calculates a geographical position of a receiver by calculating a pseudo-range between the receiver and each of a plurality of transmitters based on positioning signals outputted from a plurality of the transmitters, a detection process detects whether each positioning signal is a signal received with occurrence of multi-path, and a determination process determines a positioning error range of the geographical position based on arrangement of a plurality of the transmitters, a positioning error generated when calculating the pseudo-range and a detection result in the detection process.
Therefore, since the positioning error range of the geographical position can be calculated based on arrangement of a plurality of transmitters, the positioning error generated when calculating the pseudo-range and the detection result of multi-path, the appropriate positioning error range can be calculated taking the influence of the multi-path into consideration even if the multi-path occurs when receiving the positioning signals.
In one aspect of the present information, the positioning error is acquired based on accuracy information of the pseudo-range that said positioning signal has.
According to this aspect, the positioning error is obtained based on accuracy information of the pseudo-range that the positioning signal has.
Accordingly, the accuracy of the calculated pseudo-range can be reflected to the positioning error range, thereby calculating the appropriate positioning error range.
In another aspect of the present invention, a detection process detects an error in the pseudo-range of a positioning signal received with occurrence of multi-path, and calculates said positioning error based on the error in the pseudo-range.
According to this aspect, the detection process detects an error in the pseudo-range of the positioning signal received with occurrence of multi-path, and calculates a positioning error based on the error in the pseudo-range.
Therefore, since the positioning error range of the geographical position in the receiver can be calculated based on the error in the pseudo-range generated due to the multi-path even if the multi-path is detected when receiving the positioning signal, the influence of the multi-path can be reflected to the positioning error range, and the appropriate positioning error range can be calculated.
In further aspect of the present invention, the error in the pseudo-range of the positioning signal received with occurrence of multi-path is compared with a value obtained by using the accuracy information of the pseudo-range that the positioning signal has, and the larger value in comparison is determined as the positioning error.
According to this aspect, the error in the pseudo-range of the positioning signal received after occurrence of the multi-path is compared with a value obtained by using accuracy information of the pseudo-range that the positioning signal has, and the value larger in comparison is determined as the positioning error.
Thus, if the multi-path is detected when receiving the positioning signal, the influence of the multi-path can be reflected to the positioning error range. If it is not detected, the accuracy of the calculated pseudo-range can be reflected to the positioning error range, thereby calculating the appropriate positioning error range.
In further aspect of the present invention, the positioning error is calculated based on the error in the pseudo-range of the positioning signal received with occurrence of multi-path and the value obtained by using the accuracy information of the pseudo-range that the positioning signal has.
According to this aspect, the positioning error is calculated based on the error in the pseudo-range of the positioning signal received with occurrence of the multi-path and the value obtained by using the accuracy information of the pseudo-range that the positioning signal has.
Accordingly, the accuracy of the calculated pseudo-range can be reflected to the positioning error range, and the influence of the multi-path can be reflected to the positioning error range when the multi-path is detected, thereby calculating the appropriate positioning error range.
In further aspect of the present invention, the error in the pseudo-range of the positioning signal received with occurrence of multi-path is generated based on a differential value between a predicted value predicted by using an already calculated pseudo-range and the pseudo-range calculated by the calculating process.
According to this aspect, the error in the pseudo-range in the positioning signal received with occurrence of the multi-path is generated based on a differential value between a predicted value which is predicted by the already calculated pseudo-range and a pseudo-range calculated by calculating device.
Therefore, the accuracy of the error in the pseudo-range generated due to the multi-path can be improved, and the positioning error range calculated when the multi-path is detected can be appropriately calculated.
In further aspect of the present invention, when the differential value is less than a predetermined reference value, the value obtained by using the accuracy information is determined as the positioning error.
According to this aspect, when the differential value is less than a predetermined reference value, the value obtained by using the accuracy information is determined as the positioning error.
Accordingly, when the error in the pseudo-range caused due to the multi-path is smaller than the value obtained by using the accuracy information in the positioning signal, the positioning error range can be calculated by using the accuracy information that the positioning signal has, and hence the positioning error range can be appropriately calculated when the multi-path is accidentally detected.
The above object of the present invention can be achieved by a positioning error range setting processing program embodied on a computer-readable medium of the present invention. The program causes a computer to function as: a calculating device for calculating a geographical position of a receiver by calculating a pseudo-range between said receiver and each of a plurality of transmitters based on a positioning signal transmitted from each of a plurality of said transmitters; a detecting device for detecting whether each said positioning signal is a signal received with occurrence of multi-path; and a determining device for determining a positioning error range of said geographical position based on arrangement of a plurality of said transmitters, a positioning error generated when calculating said pseudo-range and a detection result of said detecting device.
According to the present invention, a computer calculates a geographical position of a receiver by calculating a pseudo-range between the receiver and each of a plurality of transmitters based on positioning signals transmitted from a plurality of the transmitters, detects whether each positioning signal is a signal received with occurrence of multi-path, and determines a positioning error range of the geographical position based on a positioning error generated when calculating the pseudo-range and a detection result of the detecting device.
Therefore, since a positioning error range of the geographical position can be calculated based on arrangement of a plurality of the transmitters, the positioning error generated when calculating the pseudo-range and the detection result of the multi-path, the appropriate positioning error range can be calculated taking the influence of the multi-path into consideration even if the multi-path occurs when receiving the positioning signals.
In one aspect of the present invention, the computer is caused to function so as to obtain the positioning error based on accuracy information of said pseudo-range that said positioning signal has.
According to this aspect, the computer obtains the positioning error based on accuracy information of the pseudo-range that the positioning signal has.
Accordingly, the accuracy of the calculated pseudo-range can be reflected to the positioning error range, thereby calculating the appropriate positioning error range.
In another aspect of the present invention, the computer is caused to function as the detecting device for detecting an error in said pseudo-range of the positioning signal received with occurrence of multi-path, and calculating the positioning error based on the error in the pseudo-range.
According to this aspect, the computer detects an error in the pseudo-range of the positioning signal received with occurrence of the multi-path, and calculates the positioning error based on the error in the pseudo-range.
Thus, since the positioning error range of the geographical position in the receiver can be calculated based on the error in the pseudo-range caused due to the multi-path even if the multi-path is detected when receiving the positioning signal, the influence of the multi-path can be reflected to the positioning error range, thereby calculating the appropriate positioning error range.
In further aspect of the present invention, the computer is caused to compare the error in said pseudo-range of the positioning signal received with occurrence of multi-path with a value obtained by using accuracy information of the pseudo-range that the positioning signal has, and determine the larger value in comparison as the positioning error.
According to this aspect, the computer compares the error in the pseudo-range of the positioning signal received with occurrence of the multi-path with a value obtained by using accuracy information of the pseudo-range that the positioning signal has, and determines the value which is larger in comparison as the positioning error.
Therefore, if the multi-path is detected when receiving the positioning signal, the influence of the multi-path can be reflected to the positioning error range. If it is not detected, the accuracy of the calculated pseudo-range can be reflected to the positioning error range, thereby calculating the appropriate positioning error range.
In further aspect of the present invention, the computer is caused to calculate the positioning error based on the error in the pseudo-range of the positioning signal received with occurrence of multi-path and a value obtained by using the accuracy information of the pseudo-range that the positioning signal has.
According to this aspect, the computer calculates the positioning error based on the error in the pseudo-range of the positioning signal received with occurrence of the multi-path and a value obtained by using accuracy information of the pseudo-range that the positioning signal has.
Accordingly, the accuracy of the calculated pseudo-range can be reflected to the positioning error range, and the influence of the multi-path can be reflected to the positioning error range when the multi-path is detected, thereby calculating the appropriate positioning error range.
In further aspect of the present invention, the computer is caused to generate the error in the pseudo-range of the positioning signal received with occurrence of multi-path based on a differential value between a predicted value predicted by using an already calculated pseudo-range and the pseudo-range calculated by the calculating device.
According to this aspect, the computer generates the error in the pseudo-range of the positioning signal received with occurrence of the multi-path based on a differential value between a predicted value which is predicted by the already calculated pseudo-range and a pseudo-range calculated by the calculating device.
Thus, the accuracy of the error in the pseudo-range caused due to the multi-path can be improved, and the positioning error range calculated when the multi-path is detected can be appropriately obtained.
In further aspect of the present invention, the computer is caused to determine the value obtained by using the accuracy information as the positioning error when the differential value is less than a predetermined reference value.
According to this aspect, when a differential value is less than a predetermined reference value, the computer determines the value obtained by using the accuracy information as the positioning error.
Therefore, when the error in the pseudo-range caused due to the multi-path is smaller than the value obtained by using the accuracy information in the positioning signal, the positioning error range can be calculated by using the accuracy information that the positioning signal has, and hence the positioning error range can be appropriately calculated when the multi-path is accidentally detected.